Transfer case for motor vehicles

ABSTRACT

In a transfer case the ring gear of the crown wheel and the meshing pinion are arranged on that side of the ring gear carrier of the crown wheel that faces away from the center of the differential gear of the transfer case. Stated simply, the pinion and the ring gear of the crown wheel are arranged so as to be “reflected”, that is, on the “other side” of the ring gear carrier of the crown wheel, as compared to a conventional differential gear. This feature allows the pinion shaft to be mounted rigidly and, thus, optimized for noise and efficiency.

[0001] This application claims the priority of German Patent Document No. 101 43 886.9-12, filed Sep. 7, 2001, the disclosure of which is expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] The present invention relates to a transfer case for motor vehicles.

[0003] DE 198 39 481 A1 describes a rear axle transfer case for motor vehicles that comprises a pinion, which is driven with a cardan shaft or propeller shaft and which meshes with a crown wheel. The crown wheel in turn drives a differential gear, from which two output shafts extend out of the transfer case on opposite sides. The crown wheel includes a ring gear and a ring gear holder, which is formed by the housing of the differential gear. The ring gear holder is arranged off-centered with respect to the differential gear. The ring gear of the crown wheel and the pinion are arranged on that side of the ring gear carrier that faces the “central plane” of the differential gear. In this differential gear the pinion shaft is mounted with two double row tandem angular ball bearings, which are installed in an O arrangement. The first angular ball bearing is arranged directly at the pinion, and the second, at a distance from the pinion on the pinion shaft. Thus, the pinion is mounted in “overhung” position.

[0004] In most of the conventional motor vehicles with a rear axle drive, the propeller shaft runs in a “central tunnel”, that is essentially in the center of the motor vehicle from the transmission to the transfer case towards the rear.

[0005] In some vehicles, such as an all wheel drive vehicle, described in EP 0901 423 B1, the propeller shaft runs laterally offset in relation to the central longitudinal plane of the motor vehicle. Correspondingly the transfer case is also arranged off-centered at the rear axle. Owing to the off-centered arrangement of the transfer case, two output shafts of different length are required at the rear axle, a feature that results in a more elaborate design and additional expense.

[0006] An object of the invention is to provide an improved transfer case for motor vehicles with a laterally offset propeller shaft.

[0007] The problem is solved with the invention described and claimed hereinafter.

[0008] In an embodiment of the present invention, the ring gear of the crown wheel and the engaging pinion are arranged on that side of the ring gear carrier of the crown wheel that faces away from the differential gear of the transfer case. In other words, the pinion and the ring gear of the crown wheel are arranged to be “reflected”, that is, on the “other side” of the ring gear carrier of the crown wheel, as compared to a conventional differential gear.

[0009] A result of the “reflected” arrangement of the crown wheel ring gear and of the pinion is a number of significant design advantage. First of all, the reflected arrangement of the pinion and of the crown wheel ring gear allows the lateral offset of the propeller shaft to be compensated. Another advantage is that the pinion no longer has to be mounted in a “overhung” position, as is in DE 198 39 481 A1. In the prior art, the pinion head is virtually aligned with the transfer case. In contrast, in the “reflected” arrangement, there is adequate space between the pinion head and the output shafts for a pinion bearing, a factor that is very advantageous to the rigidity of the pinion mounting.

[0010] According to a further development of the invention, the pinion shaft has two hollow cylindrical recesses, into each of which a pinion bearing is installed. One of the pinion bearings can be arranged directly “below” the pinion teeth, and the other pinion bearing “just behind” the pinion teeth. This enables an extremely rigid pinion mounting, a feature that is advantageous for many reasons. A very rigid mounting increases, for example, the service life and the efficiency of the transmission. At the same time it reduces noise emissions.

[0011] Preferably angular ball bearings, installed in an O arrangement, are used for mounting the pinion. Thus, the bearing rigidity and the efficiency of the transfer case can be further improved.

[0012] In various novel motor vehicle concepts, it is advantageous to use the central tunnel, which is the central longitudinal area of the motor vehicle, for housing various “motor vehicle components”, such as the fuel tank. Such an arrangement is advantageous, especially with respect to “derivability”. Derivability means that one basic platform can be used for different model variants, for example limousine, station wagon, and coupe, with and without just slight reconstruction.

[0013] In such motor vehicles the propeller shaft runs laterally offset in relation to the central longitudinal axis of the motor vehicle by, for example, 200 mm. According to the invention, there is a gear or a chain drive to “bridge the distance” between the offset propeller shaft and the transfer case pinion in the area of the rear axle. Thus, the transfer case can still be arranged in the center of the motor vehicle, when the propeller shaft is offset relatively far. This feature has the significant advantage that two equally long or even identical output shafts can be used.

[0014] Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic top view of the transfer case according to the invention.

[0016]FIG. 2 is a side view of the transfer case of FIG. 1.

[0017]FIG. 3 is a schematic perspective view of the transfer case of FIGS. 1 and 2.

[0018]FIG. 4 is a sectional view of the transfer case according to FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0019]FIG. 1 is a schematic drawing of a rear axle transfer case of a motor vehicle with a drive pinion 1, which meshes with a crown wheel 2. The crown wheel 2 is formed by a ring gear 3 and a ring gear carrier 4. The ring gear carrier 4 is fastened to a housing 5 of a differential gear 6 so as not to rotate.

[0020] Two output shafts 7, 8, which are connected to the wheels of the motor vehicle (not illustrated here), branch off from the differential gear 6 or from the transfer case on opposite sides.

[0021] The pinion 1 is driven by a propeller shaft 9, which is connected to the motor vehicle transmission (not illustrated) and whose end has a gear 10, which meshes with a gear 11, which is connected to the pinion 1.

[0022] As evident from FIG. 1, the propeller shaft 9 is offset laterally, that is, in the direction of the longitudinal axis 12 of the output shafts 7, 8. The distance between the longitudinal axis 13 and the “center” 14 of the differential gear 6 or the transfer case is, for example, 200 mm.

[0023] To “compensate” for this lateral offset of the propeller shaft 9, the ring gear 3 of the crown wheel 2 and the pinion 1 are arranged “reflected” with respect to the ring gear carrier 4, as compared to conventional transfer cases. That is, the ring gear 3 and the pinion 1 are arranged on that side of the ring gear carrier 4 that faces away from the transfer case 6 or the center 14 of the transfer case 6.

[0024] Another difference, compared to conventional transfer cases is that the propeller shaft 9 is not connected here coaxially to the pinion 1, but rather by the gear arrangement 10, 11. The gear arrangement 10, 11 serves to “bridge” the lateral offset of the propeller shaft and to enable an additional translation.

[0025] Owing to the “reflected arrangement” of the ring gear 3 and the pinion 1 there are still other significant advantages that are explained in detail in conjunction with FIG. 4.

[0026]FIG. 2 is a side view of the transfer case of FIG. 1. In this drawing the propeller shaft 9 runs below the output shafts 7, 8. This height differential is compensated for by the gear arrangement 10, 11 and the pinion 1, meshing with the ring gear 3.

[0027]FIG. 3 is a schematic perspective view of the transfer case of FIGS. 1 and 2. Here, too, the lateral offset and the height offset of the propeller shaft 9 can be clearly recognized.

[0028]FIG. 4 is a schematic drawing of a sectional view of the transfer case in the area of the pinion 1 and the propeller shaft 9. The end of the propeller shaft 9 is connected to the gear 10, which is mounted here with two angular ball bearings 15, 16, which are installed in an O arrangement and shown only as a schematic. The gear 10 meshes with the gear 11, which is connected as one piece to the pinion 1.

[0029] The pinion 1 is mounted by two angular ball bearings, in particular by a first angular ball bearing 17 and a second angular ball bearing 18, which are also installed in an O arrangement. As shown in FIG. 4, the pinion 1 is a “hollow pinion”. The first angular ball bearing 17 is arranged in a recess 19, and the second angular ball bearing 18 is arranged in a recess 20 of the pinion 1. The first angular ball bearing 17 sits directly below the pinion ring gear 21. In contrast, the second angular ball bearing 18 sits just behind the pinion ring gear 21, that is, in the region of the rear half of the gear 11.

[0030] The pinion mounting, depicted in FIG. 4, is different from the pinion mountings of conventional transfer cases. Namely the pinion 1 is not mounted in overhung position. The result of the two angular ball bearings 17, 18, especially the angular ball bearing 17, sitting directly under the pinion ring gear 21, is an extremely rigid pinion mounting. Compared to a pinion, mounted in overhung position, the two sided mounting of the pinion 1 results in a significant decrease in wear and a longer service life as well as better efficiency of the transmission.

[0031] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

What is claimed:
 1. A transfer case for motor vehicles comprising: a differential gear having a central plane; a crown wheel that drives a differential gear, the crown wheel including, a ring gear, and a ring gear carrier; a pinion that meshes with the crown wheel, wherein the pinion and the ring gear of the crown wheel are arranged on a side of the ring gear carrier that faces away from the central plane of the differential gear.
 2. The transfer case of claim 1, wherein the ring gear carrier is off-centered with respect to the differential gear.
 3. The transfer case of claim 1, further comprising two output shafts, which branch off from opposite sides of the transfer case.
 4. The transfer case of claim 3, wherein the differential gear is arranged in the center of the motor vehicle, and wherein the output shafts have about the same length.
 5. The transfer case of claims 1, wherein the pinion is driven by a propeller shaft which is perpendicular to the output shafts and is offset laterally with respect to a central plane of the transfer case.
 6. The transfer case of claim 1, wherein the propeller shaft is offset laterally by 150 mm to 250 mm with respect to a central longitudinal plane of the motor vehicle.
 7. The transfer case of claim 1, wherein the propeller shaft is offset laterally by 200 mm with respect to a central longitudinal axis of the motor vehicle.
 8. The transfer case of claim 1, wherein the pinion is mounted by first and second bearings.
 9. The transfer case of claim 8, wherein the pinion includes a pinion ring gear, and wherein the first bearing is arranged directly in an area of the pinion ring gear, and the second bearing is arranged behind the pinion ring gear.
 10. The transfer case of claim 9, wherein the pinion has hollow cylindrical recesses, in which the first and second bearings are arranged, respectively.
 11. The transfer case of claim 10, wherein the first bearing is arranged directly below the pinion ring gear.
 12. The transfer case of claim 11, wherein the bearings are angular ball bearings, which are arranged in an O arrangement.
 13. The transfer case of claim 12, further comprising a torque transmission unit that connects the pinion to the propeller shaft.
 14. The transfer case of claim 13, wherein the torque transmission unit includes a gear arrangement.
 15. The transfer case of claim 14, wherein the gear arrangement includes first and second gears, and wherein the first gear engages the propeller shaft, and the second gear engages the pinion.
 16. The transfer case of claim 13, wherein the torque transmission unit includes a chain drive.
 17. A method of making a transfer case for motor vehicles, the method comprising: placing a pinion of the transfer case and a ring gear of a crown wheel of the transfer case on a side of a ring gear carrier of the crown wheel, which side faces away from a central plane of a differential gear of the transfer case.
 18. The method of claim 17, wherein the ring gear carrier is off-centered with respect to the differential gear, wherein the differential gear is arranged in the center of the motor vehicle, and wherein the pinion is driven by a propeller shaft which is perpendicular to the output shafts and is offset laterally with respect to a central plane of the differential gear.
 19. The method of claim 18, further comprising supporting the pinion with first and second bearings by arranging the first bearing directly in an area of a pinion ring gear of the pinion and by arranging the second bearing behind the pinion ring gear.
 20. The method of claim 19, further comprising arranging the first bearing directly below the pinion ring gear.
 21. The method of claim 20, further comprising using a torque transmission unit to connect the pinion to the propeller shaft. 